Security inspection technology and apparatus are extensively applied to airports, railway stations, seaports, customs houses and other important sites needing security inspection to carry out inspection of bodies of persons, luggage and bulk goods and containers mainly in respect of inspection and detection of explosives, drugs and metal arms.
An ordinary technology for continuously and automatically carrying out security inspection of persons is a security inspection door which employs pulse magnetic field eddy current inspection technology. The pulse magnetic field emitted by an emitting coil generates an eddy current in a metal. A secondary induction magnetic field generated by the eddy current destroys balance of the original magnetic field, is received by a receiving coil, and generates an alarm after treatment of an electric circuit. This security inspection technology has advantages such as good reliability, high inspection efficiency and simple manipulation. However, it can be used to inspect very limited types of articles, generally can only determine whether the persons being inspected carry metal-type prohibited articles.
To effectively inspect more types of prohibited articles by a security inspection system and meanwhile ensure protecting the persons being inspected from possible radiation damages, all the countries in the world are exploring and researching more advanced security inspection technology, such as ion scanning technology and millimeter wave technology.
Of the technologies, ion mobility technology relates to collecting fine particles of a substance to be analyzed or volatilized gases as sampling gases into a detector. Then the sampling gas, subject to ionization, forms substance ions. An electric field is applied to the substance ions resulting from the ionization to make them move. Since mobility rate of the substance ions is related to ion mass, number of electric charges, size of ions and mobility environment, mobility rate of the substance ions can be considered as a parameter for identifying characteristics of substance. Since a majority of explosives and drugs can be gasified and ionized into negative ions and positive ions, ion mobility technology can be regarded as a method for security inspection, particularly for detection of trace substance.
Use of millimeter wave technology for security inspection in essence means use of the properties that the millimeter wave can permeate ordinary clothes and millimeter wave emission rate and reflection coefficient of various substances vary (metals are more distinct from other substances in this regard). Security inspection by millimeter wave technology does not have ionizing radiation, does not require complicated protection against radiation and contact with human body, so it is an ideal technology for security inspection. Nevertheless, currently the millimeter wave technology exhibits a limited resolution and can only detect larger pieces of substance. More unfavorably, the millimeter wave technology usually can do nothing about substances concealed behind metals.
In addition, in the present-day security inspection systems for persons, inspection of radioactive substances such as uranium increasingly draws people's attention. It is not only complex but also time-consuming to use an independent device to inspect persons in respect of any radioactive substances after inspection of conventional prohibited articles as mentioned above, and moreover, there is a certain hidden danger of security because various necessary security inspections cannot be simultaneously carried out.